Portable leaf blower-vacuum devices are well-known and widely used by homeowners and grounds keepers to clean outdoor areas of leaves, grass clippings and debris. A conventional leaf blower-vacuum has a high speed centrifugal fan turned by an output shaft of either an electric motor or an internal combustion engine. The fan includes an impeller enclosed within a housing having an inlet opening and an outlet opening. The motor is mounted to the fan housing and sometimes also enclosed within a separate housing. A handle enables the entire unit to be picked up and held with one hand in an elevated position above the ground.
The fan can be converted for use as either a blower or a vacuum by attaching an elongated tube to either the inlet or the outlet of the fan housing. In a blower mode, the tube concentrates air expelled through the air outlet to create a highly-directed stream of high velocity air at the end of the tube. A cover is placed over the air inlet for preventing accidental ingestion of objects while permitting a free flow of air into the air inlet. In a vacuum mode, the conventional tube is removed from the outlet. A vacuum tube, typically having a larger diameter than the concentrator tube, is attached to the air inlet after the cover is removed. Air drawn through an opening in the end of the vacuum tube tends to entrain objects loose in the vicinity of the end of the tube. The objects are carried by the flow into the fan and then discharged into a porous sack hung around the outlet to collect debris.
Since lawns tend to be relatively large, it is desirable to have a unit which has a large vacuum tube and which draws in large volumes of air. For a given fan turning with a given speed, one way to increase its capacity is to increase the size of its inlet opening. Optimizing the fans capacity by increasing the size of the inlet opening will, however, usually result in a decrease in pressure generated by the fan. A decrease in fan pressure usually means a decrease in the velocity of the air at the fan outlet. However, maximum air velocity is usually desired for the fan when it is being operated as a blower.
In a convertible leaf blower and vacuum apparatus described U.S. Pat. No. 4,694,528 of Comer et al., the diameter of the air inlet is changed by fixing a ring-shaped member to an air inlet cover, thereby automatically narrowing the diameter of the air inlet when the cover is attached over the air inlet. The ring member is disposed close to the impeller and prevents air spill between the high pressure side and low pressure side of the impeller, thus presumably increasing fan pressure and air velocity. Since the ring member must be placed in close proximity to the impeller and fit tightly against the air inlet opening to prevent a flow of air between the ring member and the air inlet, the cover must be carefully aligned with, and stably held against, the air inlet.
One problem with the unit disclosed by Comer et al. is the manner in which the cover is connected to the inlet of the fan housing. Circumscribing the periphery of the cover is a plurality of regularly-spaced locking tabs which interact with a plurality of latching tabs disposed on the outside of the fan housing around the periphery of the air inlet. The same latching tabs are used to connect to the air inlet a vacuum tube, which includes locking tabs like those of the cover. To prevent the tube from wobbling when attached to the air inlet, four latching tabs are used. Aligning all of the locking tabs with the latching tabs can prove difficult, especially when dirt builds up around the opening.